Recent advances in human islet transplantation have shown great promise as an approach to treat insulin-dependent diabetes. However, the clinical potential of beta-cell replacement therapies will not be realized until appropriate strategies have been developed for the expansion of pancreatic islets ex vivo or for stimulating new islet growth within residual pancreatic tissue of diabetic patients. It is known that certain nutrients and growth factors can induce pancreatic beta-cell growth. The ErbB receptor family plays a fundamental role in the development, differentiation, proliferation and survival of many tissues including the pancreas. ErbB receptor gene ablation studies have suggested an important proliferative role for ErbB signaling in beta-cell biology but these studies have been hindered by the severity of defects found in these receptor-null mice. Members of the EGF-related peptide growth factor family bind to and activate ErbB receptors. Each ErbB ligand has distinct ErbB receptor binding specificities and can activate unique downstream signaling pathways to generate diverse biological responses. For example, exogenous, recombinant betacellulin (BTC) can uniquely induce beta-cell neogenesis, proliferation and differentiation in both in vitro and in vivo models. However, it is important to note that endogenous ErbB ligand precursors have distinct signaling functions and that sequential processing to release soluble ligand is a fundamental regulatory event in ErbB receptor signaling; a regulatory step which can not be duplicated by addition of exogenous recombinant growth factors. The generation and viability of mice deficient in certain ErbB ligands including BTC provides important genetic tools to investigate the specific and/or complementary roles of individual endogenous ErbB ligands in beta-cell biology. The long-term objectives of my research are to determine the unique cellular and biochemical functions of different endogenous ErbB ligands in beta-cell biology. The specific goals of this grant proposal are to investigate the roles of endogenous BTC signaling in beta-cell proliferation, differentiation, neogenesis and survival. Specific aim 1 of this application will characterize the regulated and sequential processing of BTC precursor in beta cells. The second Specific aim will examine the signaling potential of different BTC cleavage products in beta-cells proliferation and differentiation in vitro. In Specific aim 3, the role of BTC in beta-cell development and neogenesis as well as maintenance of beta-cell mass in vivo will be examined utilizing Btc-/-deficient mice alone or under EGFR wa2/wa2 and/or combinatorial ErbB ligand null genetic backgrounds. The results of these studies should enhance our understanding of the role of BTC signaling in beta-cell biology and its application to human beta-cell replacement therapies.